The purpose of the requested award would be to provide the candidate with the time and resources necessary to develop into an independent investigator. A comprehensive didactic program in immunology offered by the Immunology Graduate Group will be complemented by participation in seminars, journal clubs, and other forums for presentations. Expertise in conducting research will be gained by intensive and structured laboratory work focusing on the outlined research project. These activities will take place in a highly stimulating and supportive academic environment under the supervision of an established and productive scientist. SLP-76 is a protein adapter molecule playing a critical role in T cell development and signaling through the T cell receptor (TCR). Interactions between SLP-76 and many other molecules, including the adapters GADS, VAV, and SLAP-130 have been demonstrated and studied using genetic and biochemical approaches. Despite the significant progress made in this field recently, many important aspects of the function of SLP-76 remain elusive and controversial. Specifically, knowledge about the precise temporal and spatial characteristics of SLP-76 function and interactions is lacking. I hypothesize that in T cells SLP-76 participates in multimolecular interactions in a precise spatial and temporal order that is essential for effective signaling through the TCR. To test this hypothesis and study the organization of these signaling complexes, I will use standard genetic and biochemical approaches combined with advanced microscopy imaging modalities. The localization, colocalization, and movement of signaling molecules will be visualized by fluorescent and confocal microscopy including real time imaging. To examine the structural requirements for these processes, experiments will be performed in a variety of cell lines as well as in primary murine cells from wild type and transgenic mice. Fluorescent Resonance Energy Transfer (FRET)-based techniques will be used to explore protein-protein interactions on a molecular level.